Sea level rise: what has happened so far

Sea level has been rising globally since the late 1700s. This rise has accelerated in recent decades, thanks to increased melting of glaciers and ice sheets due to a warmer climate, plus the fact that warmer oceans are less dense and expand, further increasing sea level. Though sea level rise appears to have slowed over the past five years, it will significantly accelerate if the climate warms the 2 - 3°C it is expected to this century. If these forecasts of a warmer world prove accurate, higher sea levels will be a formidable challenge for millions of people world-wide during the last half of this century. Sea level rise represents one of my personal top two climate change concerns (drought is the other). I'll present a series of blog posts over the coming months focusing on at-risk areas in the U.S., Caribbean, and world-wide. Today, I focus on the observed sea level rise since the Ice Age.

What's at stakeHigher sea levels mean increased storm surge inundation, coastal erosion, loss of low-lying land areas, and salt water contamination of underground drinking water supplies. About 44% of the Earth's 6.7 billion people live within 150 km (93 miles) of the coast, and 600 million people live at an elevation less than ten meters (33 feet). Eight of the ten largest cities in the world are sited on the ocean coast. In the U.S., the coastal population has doubled over the past 50 years. Fourteen of the twenty largest urban centers are located within 100 km of the coast, and are less than ten meters above sea level (McGranahan et al., 2007). The population of many vulnerable coastal regions are expected to double by 2050, according to the U.S. Census Bureau.

Sea level rise since the Ice AgeBefore the most recent Ice Age, sea level was about 4 - 6 meters (13 - 20 feet) higher than at present. Then, during the Ice Age, sea level dropped 120 meters (395 ft) as water evaporated from the oceans precipitated out onto the great land-based ice sheets. The former ocean water remained frozen in those ice sheets during the Ice Age, but began being released 12,000 - 15,000 years ago as the Ice Age ended and the climate warmed. Sea level increased about 115 meters over a several thousand year period, rising 40 mm/year (1.6"/yr) during one 500-year pulse of melting 14,600 years ago. The rate of sea level rise slowed to 11 mm/year (0.43"/yr) during the period 7,000 - 14,000 years ago (Bard et al., 1996), then further slowed to 0.5 mm/yr 6,000 - 3,000 years ago. About 2,000 - 3,000 years ago, the sea level stopped rising, and remained fairly steady until the late 1700s (IPCC 2007). One exception to this occurred during the Medieval Warm Period of 1100 - 1200 A.D., when warm conditions similar to today's climate caused the sea level to rise 5 - 8" (12 - 21 cm) higher than present (Grinsted et al., 2008). This was probably the highest the sea has been since the beginning of the Ice Age, 110,000 years ago. There is a fair bit of uncertainty in all these estimates, since we don't have direct measurements of the sea level.

Sea level rise over the past 300 yearsDirect measurements of sea level using tide gauges began in Amsterdam in 1700. Additional tide gauges began recording data in Liverpool, England in 1768 and in Stockholm, Sweden in 1774. These gauges suggest that a steady acceleration of sea rise of 0.01 mm per year squared began in the late 1700s, resulting in a rise in sea level of 2.4" (6 cm, 0.6 mm/yr) during the 19th century and 7.5" (19 cm, 1.9 mm/yr) during the 20th century (Jevrejeva et al., 2008). There is considerable uncertainty in just how much sea level rise has occurred over the past few centuries, though. Measuring global average sea level rise is a very tricky business. For starters, one must account for the tides, which depend on the positions of the Earth and Moon on a cycle that repeats itself once every 18.6 years. Tide gauges are scattered, with varying lengths of record. The data must be corrected since land is sinking in some regions, due to pumping of ground water, oil and gas extraction, and natural compaction of sediments. Also, the land is rising in other regions, such as Northern Europe, where it is rebounding from the lost weight of the melted glaciers that covered the region during the last Ice Age. Ocean currents, precipitation, and evaporation can cause a 20 inch (50 cm) difference in sea level in different portions of the ocean. As a result of all this uncertainty, the 1996 Intergovernmental Panel on Climate Change (IPCC) report gave a range of 4 - 10" (10 - 25 cm) for the observed sea level rise of the 20th century. The 2007 IPCC report narrowed this range a bit, to 5 - 9" (12 - 22 cm), or 1.2 - 2.2 mm/year. Rates of sea level rise are much higher in many regions. In the U.S., the highest rates of sea-level rise are along the Mississippi Delta region--over 10 mm/yr, or 1 inch/2.5 years (USGS, 2006). This large relative rise is due, in large part, to the fact that the land is sinking.

Figure 2. Absolute sea level rise between 1955 and 2003 as computed from tide gauges and satellite imagery data. The data has been corrected for the rising or sinking of land due to crustal motions or subsidence of the land, so the relative sea level rise along the coast will be different than this. The total rise (in inches) for the 48-year period is given in the top scale, and the rate in mm/year is given in the bottom scale. The regional sea level variations shown here resulted not only from the input of additional water from melting of glaciers and ice caps, but also from changes in ocean temperature and density, as well as changes in precipitation, ocean currents, and river discharge. Image credit: IPCC, 2007

Sea level rise over the past 15 yearsAccording to the Intergovernmental Panel on Climate Change (IPCC) 2007 report, sea level accelerated from the 1.2 - 2.2 mm/yr observed during the 20th century to 3.1 mm/year during the period 1993 - 2003. These estimates come from high resolution measurements from satellite radar altimeters, which began in 1992. Tide gauges showed a similar level of sea level rise during that ten-year period. The IPCC attributed more than half of this rise (1.6 mm/yr) to the fact that the ocean expanded in size due to increased temperatures. Another 1.2 mm/yr rise came from melting of Greenland, West Antarctica, and other land-based ice, and about 10% of the rise was unaccounted for. However, during the period 2003 - 2008, sea level rise slowed to 2.5 mm/year, according to measurements of Earth's gravity from the GRACE satellites (Cazenave et al., 2008). This reduction in sea level rise probably occurred because ocean sea surface temperatures have not warmed since 2003 (Figure 3). The authors concluded that sea level rise due to ocean warming decreased more than a factor of five from 2003 - 2008, compared to 1993 - 2003, contributing only 0.3 mm/yr vs. the 1.6 mm/yr previously.

Figure 3. Global average sea surface temperatures (SSTs) from 1990-2008. SSTs have not increased in the past seven years. Image credit: NASA/GISS.

Tropical updateThe tropical Atlantic is quiet, and the only region worth watching is the Western Caribbean, which could see formation of a tropical disturbance with heavy thunderstorm activity this weekend.

Quoting kimoskee:As I read the blogs about the various generators I chuckle to myself remembering after the last storm when we cranked up the genny and the neighbour complained about the noise... The complaining stopped as soon as we threw an extension cord over the fence!!! ;-)

As I read the blogs about the various generators I chuckle to myself remembering after the last storm when we cranked up the genny and the neighbour complained about the noise... The complaining stopped as soon as we threw an extension cord over the fence!!! ;-)

I think that the aftermath of a storm will be much different here in South Florida than it ever has been. Many new plans have been implemented, most people have shutters now (new construction had to come with shutters).

Grocery stores, drug stores, and gas stations at main population points throughout the county have generator power. I've even seen the generators set up next to the pumping station for the sewage.

Some of the newer red light installations have generators, and solar batteries to help in the case of a large power loss.

Quoting CybrTeddy:Question: Remember how last year the GFS had a GREAT handle on Tropical Cyclone Genesis, why isn't it like that this year? All these ghost storms yet last year, almost all of them were predicted like 2 weeks in advance by GFS first.

Yeah, I remember the GFS predicted the genesis of Bertha a week or two out.

I have a 6500W with an efficient OHV engine & big tank. I have run everything on a 3500W, (5 HP - very efficient) generator with only 110V outlet. I even ran the hot water heater, and clothes dryer (rewired, one at a time) off of it. 5 gal/day isn't hard to come by. Freeze up some gallons of water. Turn the temp way down on the fridge a couple of days B4 the storm, & remember to turn off the door heat strip (moisture control) to save the 500w.

BTW one of these will turn a decent computer into a DTV / PVR. 18V will run my laptop (3X6v or a 12v & a 6v deep cycle)very efficiently for a long time.

Question: Remember how last year the GFS had a GREAT handle on Tropical Cyclone Genesis, why isn't it like that this year? All these ghost storms yet last year, almost all of them were predicted like 2 weeks in advance by GFS first.

You can get a 10kw at BJ's wholesale for less than $2,000 with a 50 amp output plug - generac with a vanguard commercial engine. Most home AC units up to about 5 ton can run on that easily, but they use 1 gal an hour of gas.

I use that unit to power the AC to a cold level and shut it off, and I have a 4kw for the amenities and frig stuff. That unit runs for 13 hours on 4 gal. Both ratings are based upon 1/2 load. Most stuff uses the most power at startup then level off considerably. You gotta do the math and get out the meter to get the real picture of your needs.

Quoting GeoffreyWPB:Thankfully during Francis and Jeanne, I work at an establisment that I could at least bring home ice for my neighbors...would love a generator to take care of the basic needs of my neighbors. But the last time I priced, at least 6 grand for everything involved.

You can get a 10kw at BJ's wholesale for less than $2,000 with a 50 amp output plug - generac with a vanguard commercial engine. Most home AC units up to about 5 ton can run on that easily, but they use 1 gal an hour of gas.

I use that unit to power the AC to a cold level and shut it off, and I have a 4kw for the amenities and frig stuff. That unit runs for 13 hours on 4 gal. Both ratings are based upon 1/2 load. Most stuff uses the most power at startup then level off considerably. You gotta do the math and get out the meter to get the real picture of your needs.

After living here for 22 years, we invested in a generator and lexan(acrylic) and Bahama shutters (versus plywood). Not to say I would ride out a Cat 3, 4, 0r 5 (we are a block from the Gulf). It's not "if" but "when", right?

In general...for the tropics.. we prefer the GFDL..along with the GFS in the short term (out to 72hrs) after 72hrs we prefer a blend of the ECMWF and GFS or whichever has a best handle on the overall scenerio.

For North America...we prefer to use the GFS with a blend of the NAM or again..whichever has the best handel on the overall scenerio out to 72hrs. After 72 we do the ECMWF/GFS like said above.

that's good advice. IMHO, you can automate the alternating of devices with common household timers, which makes your life MUCH easier. have a power strip with several short extension cords and times, and you can set the schedule for them to alternate. then, all you have to do is watch the fuel level if you're using a gasoline-powered generator.

Quoting stormwatcherCI:I am sure they are but everything is brought in here from overseas and priced at about 100% or more profit so you can imagine. Right now we are paying about 3.40 CI for regular gas which is 4.25 US.

Quoting zoomiami:The big generators are expensive. If you own your home, and need one to stay there after a storm, the insurance will usually pay for it.

While it use to be a luxury for most people, after 05-06 it became a necessity. After living in So Fla for 30 years, that was the first time we ran our office on generator.

After living here for 22 years, we invested in a generator and lexan(acrylic) and Bahama shutters (versus plywood). Not to say I would ride out a Cat 3, 4, 0r 5 (we are a block from the Gulf). It's not "if" but "when", right?

Thankfully during Francis and Jeanne, I work at an establisment that I could at least bring home ice for my neighbors...would love a generator to take care of the basic needs of my neighbors. But the last time I priced, at least 6 grand for everything involved.

After Andrew, my mom's house came back on line in the first few days. So everybody took all their food to her house, and everyone was invited to come and eat.

When had some great meals, and shared with everybody.

Sad to say, the first responders didn't come until after all the food would have spoiled. They really have learned a lot from what happened after Andrew. It was the beginning of a different era for recovery work.

Before we got the generator, I think it was Hurri Ivan, we used all our food to feed the Emergency crews rather than waste the food. Law Enforcement loved the steaks and seafood. Cooked it on their grills. Was worth every bit of food, those guys were heroes; kept looters at bay and helped those in true need.

I had bought 5 bags of ice and put in the deep freeze with my meats so managed to keep them cold long enough to use. I live in one of the smallest districts in Cayman and it's more or less like a big family so everyone was cooking and everyone was eating. We are lucky enough to have a very wealthy woman here that helped my district tremendously with food, water and for those who didn't have their own generators. She alsohelped with a lot of the rebuilding. She runs IAMCO which helps a lot of places in the Caribbean.

Quoting stormwatcherCI:These types of generators are very pricey in Cayman and not so easy to get. I have a decent size portable but that was a luxury after Ivan. The first things I plugged in were a deep freeze for the ice, a window unit for the cold air and a couple of lights. Didn't need any more than that because due to damage to the house we were all (4) camping in one room anyway.

Good gosh, yes, ss. It's bad enough taking care of one home refrigerator after a storm-I can just imagine! Yuck!

The natural gas system never lost a second in Houston after Ike. However, if you are in an area that suffers heavy damage-like Bolivar and Galveston Island the gas company may shut-in their system. Makes the clean-up a little safer. All those gas meters buried under debris with bulldozers and backhoes running all over the place.

Before we got the generator, I think it was Hurri Ivan, we used all our food to feed the Emergency crews rather than waste the food. Law Enforcement loved the steaks and seafood. Cooked it on their grills. Was worth every bit of food, those guys were heroes; kept looters at bay and helped those in true need.